Sequence of the A-protein of coliphage MS2. III. Isolation and sequence determination of thermolytic peptides and soluble cyanogen bromide fragments: alignment of 363 amino acid residues of a total of 393.

A further and final step in the determination of the amino acid sequence of MS2 A-protein was the isolation and sequence determination of peptides obtained by thermolysin hydrolysis and the isolation and partial sequence determination of soluble cyanogen bromide cleavage products of the A-protein. With the information obtained from the tryptic, chymotryptic, thermolytic, and cyanogen bromide peptides, a total of 363 amino acid residues can be ordered unambiguously in large sequence stretches. Another 23 amino acid residues were characterized in individual peptides but could not be positioned in the Aprotein polypeptide chain without data from the nucleotide sequence of the corresponding gene (Fiers W., Contreras, R., Duerinck, F., Haegeman, G., Merregaert, J., Min Jou, W., Raeymakers, A. Volckaert, G., Ysebaert, M., Vandekerckhove, J., Nolf, F., and Van Montagu, M. (1975) Nature 256,273-278). These amino acids form the overlaps between the large stretches. The positioning of residues 261-264 and 272-274 is based entirely on data obtained from the corresponding nucleotide sequence (Fiers, W., Contreras, R., Duerinck, F., Haegeman, G., Merregaert, J., Min Jou, W., Raeymakers, A., Volckaert, G., Ysebaert, M., Vandekerckhove, J., Nolf, F., and Van Montagu, M. (1975) Nature 256, 273-278). The complete sequence of the A-protein as based on our studies and the nucleotide sequence studies is: